In the context of the present invention, the term “hot liquid” is intended to denote a liquid which, at the time it is poured into the container, has a temperature of at least 60° C., and more particularly, although not exclusively, has a temperature within the top of the range, of at least 85° C. and possibly as much as 90-95° C.
It will be recalled that a hot liquid has a substantially greater volume than the volume it occupies when it is cold. Consequently, when a container is filled with a hot liquid and then closed in a sealed manner, the liquid reduces in volume as it cools. owing to the sealing provided by the closure of the container, the reduction in volume of the liquid cannot be compensated for by admitting an equivalent volume of air. Furthermore, a comparable phenomenon occurs with the air contained in the container which, following closure, heats up in contact with the liquid and subsequently cools, with the result that finally its pressure decreases. The container is thus placed under vacuum and is deformed with an inward caving of its walls, particularly the walls of its body. By way of example, in a 1.5-liter container the reduction in volume may be around 5 to 6 cl, this being sufficient to significantly deform the container. Furthermore, as will be readily understood, the degree of reduction in volume of the liquid, and therefore the degree of concomitant deformation of the container, will be greater the higher the temperature of the liquid during filling.
In a container which is not specifically suitable, it is the weakest walls or wall parts which deform, and these deformations cannot be controlled, which means that a container deformed in these circumstances not only has a poor appearance but can also be rendered unstable if its base has been curved.
Moreover, given that a normal and natural physical phenomenon is involved, it is not conceivable to attempt to produce non-deformable containers, something which could only be achieved, insofar as is possible, by providing the walls with considerable thicknesses: this would result in a high consumption of material, and therefore in an excessive cost which is unacceptable in an industrial manufacturing process involving very large quantities. Furthermore, a container thus produced and filled under these conditions would be under vacuum, with a risk of the container bursting, particularly in the event of impact, and/or a risk of liquid spraying out when opening the container.
It is therefore known to produce containers which are specifically configured to be filled with a hot liquid, these containers being provided with parts designed to be able to deform without adversely affecting the shape of the rest of the container, particularly its base. Containers with controlled deformation which keep their general shape and which, above all, remain stable are thus formed. These deformable parts generally take the form of recessed panels provided on the body of the containers, these panels being distributed over the periphery of the body and separated from one another by portions of the body that form non-deformable beams. The panels are often substantially rectangular or approximately rectangular in shape, are possibly provided with reinforcing projections, and are elongated parallel to the axis of the container.
In some cases, such containers have a relatively high degree of deformability in the central region and are not acceptable to be sold.
Furthermore, such panel-type containers have an esthetically questionable appearance.